JP2011502222A - Method and apparatus for heating a catalyst disposed in an exhaust gas region of an internal combustion engine - Google Patents

Abstract

An internal combustion engine is operated with direct fuel injection into the combustion chambers. Furthermore, the internal combustion engine is operated with sub-optimum ignition angle efficiency and an apportionment of a fuel quantity, which is to be injected before the start of a combustion, into at least two partial injections. A torque loss which results from the sub-optimum ignition angle efficiency and/or from the apportionment of the fuel to be injected is compensated by means of an increased charge of the combustion chambers. The fuel quantity and the charge are coordinated with one another in such a way that the air ratio lambda of the combustion chamber charges is greater than 1. The method is characterized in that a measure for a temperature of the catalytic converter, in particular a measure for the temperature at the inlet of the catalytic converter, is determined and in that a quantity of reducing exhaust-gas constituents is increased by means of at least one intervention into the control of the internal combustion engine if the measure for the temperature exceeds a predetermined temperature threshold value. The approach according to the invention permits rapid heating of the catalytic converter, wherein the hydrocarbon emissions when the catalytic converter is cold are at the same time as low as possible.

Description

  The invention relates to a method for heating a catalyst arranged in the exhaust gas region of a combustion process, in particular an internal combustion engine, based on the superordinate concept of the independent claims, and an apparatus for carrying out this method.

  The internal combustion engine is operated by direct fuel injection, in which the ignition angle is delayed and the fuel injection before ignition is divided into at least two partial fuel injections for heating the catalyst. The torque loss caused by this measure is compensated by the increased cylinder filling efficiency. Under a cold catalyst that still cannot be converted, in order to achieve low exhaust emissions of the internal combustion engine, in some cases, the excess air ratio is set to lambda> 1, i.e. the internal combustion engine is operated with lean fuel / Operation with an air-fuel mixture is performed.

  Such a method and such a control device are already used in mass production. According to the known method, for example, under a cold catalyst after the start process of the internal combustion engine, changing the output of the internal combustion engine or the idling speed, for example 1200 / min, which may be increased at the stage after the start. Instead, measures are taken to generate as much heat as possible in the exhaust gas.

  This is achieved by injecting a first part of the fuel quantity in the intake stroke and a second part of the fuel quantity in the compression stroke in the method used there. The result is a stratified fuel distribution in the combustion chamber with a relatively rich and thus ignitable fuel / air mixture region near the spark plug resulting from the injection of the second part. . Such operation of the internal combustion engine can be referred to as homogenous split operation (Homogen-Split-Betrieb), where “split” is related to splitting of the injection.

  Filled air stratification allows very late ignition timing within 10-30 ° after OT (OT = top dead center) under stable engine speed and controllable exhaust gas untreated emissions . Slow ignition timing results in relatively poor ignition angle efficiency. Here, the ignition efficiency is understood to be the ratio of the torque generated under the slow ignition timing and the torque generated under the optimal ignition timing. Torque loss resulting from poor ignition timing efficiency is compensated by increasing the combustion chamber filling efficiency of the internal combustion engine. Under the realized ignition angle, the combustion chamber charging efficiency is increased to a value of about 75% of the maximum charging efficiency possible under the reference conditions. As a result, a relatively large amount of exhaust gas is generated as a whole, and the temperature is relatively high due to poor ignition angle efficiency, so that a maximum heat flow (enthalpy flow) is generated in the exhaust gas region.

  When heating by this maximal enthalpy flow, the exhaust gas region must be fully heated from the exhaust valve to the catalyst. The heat capacity of these components, especially in the case of an internal combustion engine with an exhaust gas turbocharger, results in an excessively high heat loss before the catalyst, making it difficult to effectively heat the catalyst. Furthermore, in the case of an internal combustion engine with an exhaust gas turbocharger, if the exhaust gas manifold in the exhaust gas flow path in front of the turbocharger turbine maximizes the exhaust gas enthalpy, it will increase more rapidly. When heated, the problem is that it is heated to a temperature that may cause its destruction. This constrains the maximization of the desired exhaust gas enthalpy for catalyst heating.

  The above-described homogeneous division operation of the internal combustion engine can be employed in the after-start stage at a constant timing of the fuel injection timing and the ignition timing. In the conventional internal combustion engine control device, in the after-start stage after the start operation, the rotational speed of the internal combustion engine exceeds a rotational speed threshold that is between the starter rotational speed and the idling rotational speed of the internal combustion engine, and is determined in advance. It begins when it lasts for a time interval of typically 20-30 seconds. During this time interval, the pre-catalyst located near the internal combustion engine usually reaches an operating temperature (light-off temperature) at which the conversion of harmful substances, in particular the conversion of hydroxides, is sensibly started. According to the usual definition, this light-off temperature means that 50% of undesirable exhaust gas components such as carbon monoxide (CO) and hydrocarbon (HC) appearing in front of the catalyst are harmless such as water and carbon dioxide. This is the temperature converted to the exhaust gas component.

  In practice, the percentage of hazardous substance conversion does not increase rapidly but rather increases slowly. After the start of toxic substance conversion in the pre-catalyst, the concentration of hydrocarbons measurable behind the pre-catalyst rapidly decreases towards a value close to zero. According to tests, the decrease in hydrocarbon concentration behind the pre-catalyst correlates with the arrival of the light-off temperature in the central region of the pre-catalyst. Thus, after a cold start of the internal combustion engine or after, for example, a fuel cut-off (operation of the internal combustion engine without fuel supply) during overrun, the amount of hydrocarbons discharged into the environment will reach the operating temperature of the catalyst. Depends heavily on the time interval needed for.

  Under the background as described above, an object of the present invention is to provide a method enabling rapid heating of a catalyst and an apparatus for carrying out the method.

  According to the invention, a measure for the temperature of the catalyst is measured and the amount of exhaust gas component to be reduced is raised by intervention in the control device of the internal combustion engine when the catalyst temperature exceeds a predetermined threshold, That is done.

  An internal combustion engine is operated with a lean fuel / air mixture under a cold catalyst that still cannot be converted, so that only the smallest possible untreated exhaust gas emissions such as unburned hydrocarbons are in the environment. Is not discharged. During this operating state of the internal combustion engine, heating of the catalyst is achieved by reducing the efficiency of the internal combustion engine.

Only when a predetermined temperature threshold of the catalyst temperature is reached, the amount of exhaust gas component to be reduced is raised by intervention in the control device of the internal combustion engine.
It has been shown that this measure reduces the time to reach the light-off temperature and thereby the amount of hydrocarbons released into the environment. This advantageous effect is that, even though the temperature in the central region of the catalyst is still quite low and still below the operating temperature range of the catalyst, It is considered that the conversion is already started when the temperature at the inlet of the catalyst exceeds a predetermined threshold.

  The raised supply of exhaust gas components to be reduced combined with the oxygen present in the exhaust gas initiates an exothermic reaction on this surface element, which is direct and direct, thus Contributes to accelerated catalyst heating. The heat generated in the catalyst is continuously increased by increasing the amount of the exhaust gas component to be reduced, for example, continuously. Thereby, the first few centimeters of heating of the accelerated catalyst is heated by a constant enthalpy flow from combustion in the engine, which is utilized in the prior art case (and also before the temperature threshold is exceeded in the present invention). Is much more effective than This is inter alia related to the fact that the enthalpy stream suffers losses due to the warming of other components before entering the catalyst. For example, such other components include an exhaust gas manifold, a turbocharger, and the like.

Another important advantage of the approach according to the invention is that in addition to reducing the emission of unburned exhaust gas components to be reduced, there is also a reduction in nitrogen oxide emissions.
Advantageous extensions and embodiments of the technique according to the invention will become apparent from the appended claims.

According to one embodiment, the amount of exhaust gas component to be reduced is achieved by returning the ignition angle delay.
As an alternative or in addition, according to one embodiment, the amount of exhaust gas component to be reduced is achieved by changing a predetermined fuel amount division prior to ignition in the fuel partial injection.

  Further alternatively or additionally, according to one embodiment, the amount of exhaust gas component to be reduced is achieved by lowering the excess air lambda to the side opposite the lower excess air start point. The

Further alternatively or additionally, at least one fuel post-injection can be performed after the start of combustion.
In particular, within the framework of an embodiment with at least one fuel post injection, the following advantages arise: Maximizing the exhaust gas enthalpy significantly improves the preparation and vaporization of the fuel dosed by the other injections, thereby reducing the probability that the fuel will reach the catalyst in the form of droplets. Even if the exhaust gas enthalpy is raised due to delayed ignition and increased internal combustion engine charging efficiency, it is again lowered by vaporization of the amount of fuel dosed. However, from the standpoint of desirable heating of the catalyst, this reduction is more than compensated for by more effective heating of the catalyst by an exothermic reaction. In the case of an internal combustion engine with an exhaust gas turbocharger, maximizing the exhaust gas enthalpy provides the additional advantage of protecting the manifold against overheating that may occur without additional fuel dosing. This additional injection associated with the minimum pre-catalyst temperature reduces the temperature in front of the turbocharger, which protects the manifold, and still at least one fuel to heat the catalyst. It has the dual effect of providing more energy than without post-injection.

The device according to the invention for the implementation of this method relates first to a specially tailored control device including means for carrying out this method.
The control device preferably includes at least one electrical memory in which process steps are stored as a control device program.

The control device program according to the invention assumes that all steps of the method according to the invention are carried out when it is executed on the control device.
A control device program product according to the invention with program code recorded on a machine-readable medium implements the method according to the invention when the program is executed on the control device.

  FIG. 1 shows an internal combustion engine 10, which is specifically provided with at least one combustion chamber 12 movably sealed by a piston 14. The air-fuel mixture consisting of fuel and air in the combustion chamber 12 is ignited by the spark plug 16 and then combusted. In an advantageous embodiment, the internal combustion engine 10 is optimized for the injection-controlled combustion method (strahlgefuhrte Brennverfahren). The combustion method is a method of mixture formation and energy conversion in the combustion chamber. In the injection-controlled combustion method, fuel is injected directly around the spark plug and vaporized there. This approach requires precise positioning of the spark plug 16 and fuel injector and precise injection direction in order to ignite the air-fuel mixture at the correct time. The exchange of charge in the combustion chamber 12 is controlled by gas exchange valves 18 (intake valves) and 20 (exhaust valves) that are opened and closed in phase synchronization with the movement of the piston 14. Various techniques for the operation of gas exchange valves 18 and 20 are left to those skilled in the art and are not shown in detail in FIG. 1 for clarity. When the intake valve 18 is opened and the piston 14 is moving downward, that is, during the intake stroke, air flows from the intake system 22 into the combustion chamber 12. Fuel is dosed into the air in the combustion chamber 12 through the injector 24. Exhaust gas resulting from the combustion of the combustion chamber charge is pushed into the exhaust gas system 26 when the exhaust valve 20 is opened, in which the exhaust gas system is provided with at least one catalyst 28, which The catalyst is designed, at least in part, such that catalyst 28 catalytically supports the oxidation reaction between oxygen and the reducing component of the exhaust gas. In general, the exhaust gas system 26 includes a plurality of catalysts, such as a pre-catalyst installed near the engine, such as catalyst 28 in the illustrated embodiment, and a remote catalyst, such as a three-way catalyst or NOx. And another catalyst 30 which can be an occlusion type catalyst.

  In the embodiment of FIG. 1, the internal combustion engine 10 includes a turbocharger 29 disposed in the exhaust gas flow path between the manifold 31 and the catalyst 28. As already mentioned, in such an internal combustion engine special advantages arise from the combination of the protection of the manifold and the accelerated heating of the catalyst 28. However, it should be understood that the present invention is not limited to application to an internal combustion engine with a turbocharger. This is because the advantage of accelerated heating of the catalyst 28 also occurs in the case of the internal combustion engine 10 without the exhaust gas turbocharger 29.

  The internal combustion engine 10 or the combustion in the internal combustion engine 10 is controlled by the control device 32, which processes the signals of the various sensors that reflect the operating parameters of the internal combustion engine 10 for this purpose. According to FIG. 1, these signals include the angular position of the crankshaft of the internal combustion engine 10 KW, the rotational angle sensor 34 for measuring the position of the piston 14, and the air mass mL flowing into the internal combustion engine 10. There is an air mass meter 36 to measure, and optionally a plurality of exhaust gas sensors 38, 40 that measure the concentration of exhaust gas components and / or the temperature T of the exhaust gas.

  In the embodiment of FIG. 1, the exhaust gas sensor 38 is a lambda sensor that measures the oxygen concentration in the exhaust gas as a measure of the excess air ratio L (L = lambda), whereas the sensor 40 measures the exhaust gas temperature T. . In the illustrated embodiment, the sensor 40 measures the exhaust gas temperature T at the inlet of the catalyst 28. As is well known, the excess air ratio lambda is defined as a quotient in which an air mass that can be actually used is a numerator and an air mass necessary for theoretical combustion of a certain amount of fuel is a denominator. Thus, an excess air lambda greater than 1 indicates an excess of air, whereas an excess air lambda less than 1 indicates an excess of fuel. If the exhaust gas system 26 is provided with an exhaust gas temperature sensor 40, this sensor can also be arranged at another location of the exhaust gas system 26, for example at the inlet of another catalyst 30. This is especially true when the other catalyst 30 is a NOx storage catalyst.

  What is important for the present invention is that a measure for the temperature T of the catalyst 28, 30 is measured, in particular a measure for the temperature at the inlet of the catalyst 28, 30. In the case of the embodiment as shown in FIG. 1, this measurement can be performed by measurement with the temperature sensor 40. In the case of the embodiment shown in FIG. 1, the temperature sensor 40 measures the exhaust gas temperature, especially at the inlets of the catalysts 28, 30, as a measure for temperature. As an alternative or in addition, a measure for the temperature T of the catalyst 28, 30 can be obtained by using the relationship stored in the control device 32 by the calculation model of the control device 32 from at least one operating parameter of the internal combustion engine 10. It can also be measured. When the temperature sensor 40 is located elsewhere in the exhaust gas system 26, a measure for the temperature T of the catalysts 28, 30 and in particular a measure for the temperature T at the inlet of the catalyst 28, 30 is the exhaust gas system 26. From a computational model adapted to the temperature measured elsewhere. Similarly, the calculation model can also be used to modify the temperature sensor 40 signal. This embodiment is particularly advantageous in the case of a sudden temperature change of the exhaust gas, which can be better taken into account by the calculation model due to the inertia of the temperature sensor 40.

  From the signals of these sensors and possibly other sensors, the control device 32 generates a control signal for controlling the actuator for controlling the internal combustion engine 10. In the embodiment of FIG. 1, these control signals include, among other things, a control signal S_L for controlling the throttle valve actuator 42 that adjusts the angular position of the throttle valve 44 in the intake system 22, and the controller 32 is an injector. There is a signal S_K used to control 24 and a control signal S_Z used by the control device 32 to control the spark plug 16 or the ignition device 16.

  In other respects, the controller 32 is tailored and specifically programmed to implement the method presented herein and / or one embodiment thereof and / or to control the corresponding process flow. In this case, the program is stored in at least one storage device not shown in detail in FIG.

  In the preferred embodiment, the control device 32 converts the output request for the internal combustion engine 10 into a target value relating to the torque to be generated as a whole by the internal combustion engine 10, and this torque is controlled by the control signal S_L for filling control, fuel dosing Is divided into a plurality of torque components that can be influenced by the control signal S_K for control and the control signal S_Z for ignition control. The split component of the filling is adjusted by a corresponding adjustment of the throttle valve 42 using the control signal S_L. The fuel split component mainly uses the control parameter S_K to split the fuel quantity to be injected and the fuel quantity to be injected into one or a plurality of partial injections, and between the plurality of partial injections and the piston 14. Is adjusted by the relative position with respect to the movement, and thus the injection timing. The maximum possible torque under a given air charge is obtained at the optimum excess air lambda, optimum injection timing, and optimum ignition angle.

  Before the embodiment of the method according to the invention, which will be further described below, the situation in the case of the known method is first described with reference to FIG. Looking in detail, FIG. 2 a shows the relative changes 46, 48, and 50 over time, the rotational speed n of the internal combustion engine 10 (graph 46), the temperature T of the catalysts 28, 30, in particular the catalysts 28, 30. The temperature T at the inlet of the engine, in particular the exhaust gas temperature T at the inlet of the catalyst 28, 30 (graph 48) and, for example, after the after start phase after a cold start of the internal combustion engine 10 or for example the fuel supply is cut off. The temperature (graph 50) in the central region of the catalysts 28, 30 after the coasting operation of the internal combustion engine 10 is shown. In that case, the temporal changes 48, 50 shown in FIG. 2a represent the implementation of a known method based on the expansion of the heat flow in the exhaust gas.

  At time t0, the starter accelerates the internal combustion engine 10 to a starter speed slightly above 200 rpm. With the start of combustion in the combustion chamber 12, the rotational speed n of the internal combustion engine 10 further increases, and exceeds the start / end rotational speed threshold of about 400 rpm at time t1. Next, the rotational speed n rapidly increases toward an idling rotational speed of about 1,200 rpm. The after-start phase starts at time t1 when the start / end rotation speed threshold is exceeded. In order to generate a large heat flow in the exhaust gas at the after-start stage, the control device 30 sends out the next best ignition angle through the control parameter S_Z. This sub-optimal ignition angle results in torque loss through the reduced ignition angle efficiency, which is compensated by the increased charging efficiency of the combustion chamber 12 generated by the control signal S_L. Due to the supplementary influence of the fuel control signal S_K, the excess air lambda is adjusted in the region beyond the theoretical value as a whole, so that the excess air lambda L is greater than 1, for example L = 1.1. .

  This is the only possibility for the catalyst 28, 30 to reduce hydrocarbons at all or only a small amount of hydrocarbons and thus reduce emissions of hydrocarbons sent to the environment. Is particularly important at the stage where there is only a reduction in the raw emissions of the internal combustion engine 10. This reduction occurs as a desirable result of operation with an excess air ratio lambda L greater than one.

  The increased charge efficiency produces a high exhaust gas volume, which is further at a relatively high temperature due to sub-optimal ignition angle efficiency and is in excess of oxygen. As a result, a large heat flow or enthalpy flow is generated as a whole. Thereby, the temperature T rises relatively rapidly, especially in the region of the inlets of the catalysts 28, 30, which is shown by a relatively sharp rise in the graph 48. As a result, an exhaust gas temperature of, for example, 400 ° C. has already been reached, especially at the inlets of the catalysts 28, 30, at time t2. In contrast, the temperature in the central region of the catalysts 28, 30 shown in the graph 50 reaches a temperature value of, for example, 400 ° C. for the first time at a later time t3, which is much higher than in the graph 48 This is shown by the rising of the flat graph 50. The flatter graph 50 is in front of the central region of the catalysts 28, 30, and is generated by the heat capacity of the region that is heated in front of the central region and takes heat away from the exhaust gas when the exhaust gas passes through. A typical time interval between time points t2 and t3 is on the order of 10 seconds.

  FIG. 2 b shows the temporal change in the hydrocarbon concentration before and after the front catalyst 28. The hydrocarbon concentration graph 52 in front of the pre-catalyst 28 has a maximum value 54 that protrudes first. This maximum value is directly increased from the start of the internal combustion engine 10 and the idling speed increased (for example, 1,200 rpm). Is related to the first rise of the rotational speed n to the value of. Next, the hydrocarbon concentration in front of the catalysts 28, 30 rapidly decreases toward a relatively constant value.

  In the graph 56 of the hydrocarbon concentration behind the catalysts 28, 30, the protruding maximum value 54 of the graph 52 is drawn in a crushed and expanded form over time. This crushing and stretching is not a conversion, but rather is related to some kind of accumulating action of the catalysts 28,30. Next, the hydrocarbon concentration behind the catalysts 28, 30 takes the same value as that appearing before the catalysts 28, 30, and then gradually increases due to the conversion capacity of the catalysts 28, 30. As it goes, it decreases towards a value close to zero, which is true around time t4 after time t3. That is, from the time point t4, the almost constant untreated hydrocarbon discharge of the internal combustion engine 10 is almost completely converted by the catalysts 28 and 30 that are ready for operation at that time.

  The amount of hydrocarbons discharged into the environment is proportional to the integral value of the hydrocarbon concentration behind the pre-catalyst 28. After the time point t4, there is almost no further hydrocarbon emission after the catalysts 28, 30, so that the integral value at the time point t4 also dominates the results of the exhaust gas test. In order to improve the results of such tests and thereby reduce hydrocarbon emissions into the environment, the present invention has already been implemented, especially before time t3 when the central region of the catalysts 28, 30 reaches the operating temperature. In addition, a conversion which is started earlier because of the higher exhaust gas temperature there already at the inlet of the catalyst 28, 30 is provided for faster heating of the catalyst 28, 30.

  According to one embodiment of the method according to the invention, after the start of combustion of fuel in the internal combustion engine 10, especially when the temperature T at the inlet of the catalyst 28, 30 exceeds a predetermined threshold T_S. At least one fuel post injection is performed. In the example shown here, the post-injection takes place at time t2 when the temperature threshold T_S is, for example, 400 ° C.

  FIG. 3 shows a plurality of injection models appearing in the implementation of the method according to the invention with at least one fuel post injection. At that time, the injection pulse widths ti_1, ti_2, and ti_3 are written as high levels on the crankshaft angle ° KW of the operating cycle from the intake stroke Takt_1, the compression stroke Takt_2, the operating stroke Takt_3, and the exhaust stroke Takt_4, respectively. Yes. Top dead center is indicated by OT.

  FIG. 3a shows the first for a homogeneous split operation for maximized exhaust gas enthalpy including a first partial injection ti_1 performed in the intake stroke Takt_1 and a second partial injection ti_2 performed thereafter. The injection model M_1 is shown. The second partial injection ti_2 is performed before ignition started at the crankshaft angle KW_Z. As already mentioned, the crankshaft angle KW_Z is very slow in some circumstances and is in the region from 10 ° to 30 ° after top dead center OT, so the second partial injection is also all or one. It may be performed in the part operation stroke Takt_3. However, it is done before ignition. Instead of dividing into two partial injections, the amount of fuel injected by the first injection model M_1 can be divided into three or more partial injections. The possibility of splitting is limited by the small dose capability of the injector 24. What is important in model M_1 is that the first of the partial injections divided at least twice is preferably in the intake stroke Takt_1, and the latter is before ignition in the same operating stroke, In this case, the overall excess air ratio lambda L is larger than 1.

  FIG. 3b shows a second injection model M_2 that differs from the first injection model M_1 by a fuel post-injection ti_3 performed after ignition. Therefore, the amount of fuel injected by at least one fuel post-injection ti_3 is at least no longer completely burned in the combustion chamber 12 and reaches the exhaust gas enthalpy flow maximized as the amount of unburned fuel. The vaporization enthalpy reduces the exhaust gas enthalpy somewhat, which protects, for example, the manifold 31 from overheating. The vaporized fuel is carried along with the exhaust gas stream into the catalysts 28, 30 where it is released heat by an exothermic reaction with oxygen from an exhaust gas having a composition that otherwise exceeds the theoretical value. Bring. In the preferred embodiment, the total amount of fuel injected by the injection model M_2 results in an excess air lambda L that is 1 to 3% lower than the excess air lambda L for the injection model M_1 before the catalyst. Will be metered.

  FIG. 4 shows a flow chart as an embodiment of the method according to the invention. In step 58, the start program SP is executed when the starter is operated. At this time, control parameters S_L, S_K, and S_Z that can start the internal combustion engine 10 by starting the starter are sent out. In step 60, it is checked whether or not the rotational speed n of the internal combustion engine 10 exceeds the start / end rotational speed n1. If not (n), the program returns to step 58 and the star and program 58 are further executed.

  As soon as the start / end speed n1 is exceeded (y), the program proceeds to step 62, where the flow of the after-start program NP for controlling the internal combustion engine 10 in the idling state is started. The variable t is set to the value t1. Under this value, the start / end rotation speed threshold value n1 is over. At that time, the operation by the after-start program NP first generates a large enthalpy flow in the exhaust gas in association with unburned effluent such as HC and CO which has as little exhaust gas components as possible to be reduced. The This enthalpy flow preferably allows the amount of fuel injected per combustion chamber charge to be reduced in the first stage of the intake stroke in relation to the reduced ignition angle efficiency and the increased air charge efficiency of the combustion chamber 12. Increased by dividing into injection and second injection in compression stroke. In other words, in step 62, the flow of the after-start program NP is started by the injection model M_1 as described in connection with FIG.

  In this case, dividing the amount of fuel to be injected into two injections is to increase the ignition angle efficiency by moving the ignition to the region between the crankshaft angle 10 ° to 30 ° after the top dead center OT. It offers the possibility of a relatively large reduction, which makes it possible to increase the corresponding air filling efficiency for torque loss compensation. In order to keep the unburned, untreated exhaust gas components to be reduced as low as possible, the excess air lambda L at the start of the after-start program NP is a lambda value greater than 1, for example lambda = 1. 1 is adjusted. Such an operation corresponds to the homogeneous division operation already described above.

  In the further flow of execution of the after-start program NP, in step 64 a measure for the temperature T of the catalysts 28, 30 is measured, in particular a measure for the temperature T at the inlet of the catalysts 28, 30. As already explained, this measurement is made by measurement and / or modeling.

  In step 66, the time variable t is increased by the increment dt. In step 68, the measure for temperature T measured in step 64 is compared to a temperature threshold T_S. If the temperature measure T is smaller than the temperature threshold T_S, it is presumed that the first catalyst surface element at the inlet of the catalyst 28, 30 is still unable to convert any exhaust gas components to be reduced. The query at step 68 is answered correspondingly with a negative “n” and the program then branches to step 70 where it is determined whether the maximum after-start time length t_max has been reached. Checked. A typical value for this maximum time length t_max is between approximately 20 seconds and 30 seconds.

  If the inquiry at step 70 is affirmative “y”, the program proceeds to step 72 and the main program HP for controlling the internal combustion engine 10 is executed. This main program HP differs from the after-start program NP in that the internal combustion engine 10 is no longer operated using the enthalpy flow in the exhaust gas that has been maximized.

  At the beginning of the after-start phase, the query at step 70 is still answered “n” and the program returns to steps 64 and 66 where a measure for temperature T is again obtained and the time variable t is further determined. Increased by one increment dt. In this way, the loop from step 64 to step 70 is repeatedly executed until the stop condition of step 68 or the stop condition of step 70 is satisfied. This is especially true when the internal combustion engine 10 has a large enthalpy flow and at the same time as little hydrocarbon as possible after the normal cold start, until the query of step 68 is answered “y” in the after-start program NP. It means that it is driven by emissions. As a measure for the temperature T, the elapsed time after the start can also be used. In another embodiment, this time after weighting with the temperature of the internal combustion engine 10 immediately before, during, or just after the start can be used as a measure for temperature. The lower this temperature, the smaller the weighting factor should be chosen.

  According to another embodiment, the method according to the invention can be carried out independently of the starting process of the internal combustion engine 10. In addition to the cold start of the internal combustion engine 10, the cooling of the catalysts 28, 30 occurs also during the operation of the internal combustion engine 10 under the coasting cutoff when the supply of fuel is stopped. 30 new heating steps are required. In this case, the method described in connection with the start process is eliminated, and the method according to the present invention is mainly temperature-controlled. In this case, whether or not the temperature threshold value T_S is exceeded for the temperature-related measure. A check is made. In addition to temperature control, other characteristic parameters may be taken into account, such as, for example, the identification of a cut-off during overrun.

  The inquiry at step 68 is answered “y” if the temperature T exceeds the temperature threshold T_S. In a preferred embodiment, this threshold T_S is an exhaust to be reduced by initiating an exothermic reaction with the oxygen supply in the exhaust gas by the catalyst on a scale that is preliminarily felt for the first surface elements of the catalysts 28, 30. It is determined to be equal to the temperature at which the conversion of the gas component starts. In order to make the reaction heat released by this exothermic reaction highly utilized for accelerated heating of the catalysts 28, 30, the operation of the internal combustion engine 10 is activated in step 74, among which At least one more fuel post-injection after the start of combustion. Accordingly, the after-start program NP is executed using the injection model M_2 as described in connection with FIG. 3b.

  In addition to or as an alternative to at least one fuel post injection, other measures may be taken by intervention in the control of the internal combustion engine 10 to increase the amount of exhaust gas components to be reduced.

In addition or as an alternative, for example, reducing the ignition angle delay and thus slightly increasing the ignition angle efficiency.
In addition or as an alternative, for example, the distribution of the amount of fuel dosed in individual fuel partial injections is changed.

As an additional or alternative approach, for example, the excess air lambda L is adjusted to be somewhat leaner.
It depends on the configuration of the internal combustion engine 10 which of these measures is maximally effective when used alone or in combination with other measures. Thus, individual actions or combinations of actions should be identified by testing and programmed accordingly. During the implementation of this method after answering “y” in step 68, the excess air lambda L is continuously increased from 1 to 3%, for example from lambda L = 1.1 to lambda L = 1.08. Lowering is considered a particularly appropriate measure.

  Reduction in ignition angle delay also results in an increase in HC untreated emissions. Tests with the internal combustion engine 10 have shown, for example, that a reduction in ignition angle delay may result in an approximately 3% increase in HC raw emissions. In that case, the exhaust gas temperature must be lowered in some cases.

  The excess air lambda can be increased by increasing the total amount of fuel injected by two fuel partial injections. As an alternative, the distribution of the amount of fuel that is dosed in individual fuel partial injections can be changed.

  In step 76 following step 74, the time variable t is increased by an increment dt. In step 78, in the same manner as the inquiry in step 70, it is checked whether the time variable t has exceeded the threshold value t_max after being raised several times in increments dt. If the threshold has not been exceeded, the query at step 78 is answered with "n" and the program returns to step 74 where operation continues with the second injection model M_2. In the case of one embodiment, the amount of fuel injected by another partial injection ti_3 is continuously raised at that time, and thereby advances further into the catalyst 28, 30 as the heating progresses. Adapted to the conversion ability to go. In one embodiment, the increase in unburned exhaust gas component emissions caused by at least one fuel post-injection ti_3 ends when the time threshold t_max in step 78 is exceeded. In this case, the after-start phase or the method according to the invention in general is finished, and the program is advanced to step 72, in which the main program HP for the control of the internal combustion engine 10 already described is present in the exhaust gas. Performed without increasing enthalpy flow.

  The broken line graph 80 in FIG. 2a qualitatively shows the effect of the present invention. Similar to the graph 50, the broken line graph 80 shows the temporal change of the temperature T in the central region of the catalysts 28 and 30 in the after-start stage or the normal catalyst heating operation. As shown, the movements of graphs 50 and 80 are parallel or the same up to time t2. The reason is that there is no difference from the known method until time t2. That is, especially in the case of the present invention, at the start of the after-start phase or at the start of the catalyst heating measure, the internal combustion engine 10 is operated with an increased enthalpy flow and simultaneously with as little untreated exhaust as possible of unburned exhaust gas components. Is done. The difference between the graph 50 obtained in the case of the known method and the graph 80 obtained according to the method according to the invention starts from the time t2 when the temperature T reaches the temperature threshold T_S. In one embodiment, this temperature threshold T_S is, for example, between 380 ° C. and 420 ° C. This value depends to a large extent on the catalysts 28, 30. At time t> t2, only the increased enthalpy flow, combined with the conversion capacity of the raw discharge of raw hydrocarbons, which is increased in the framework of the invention, starts at least at the inlet of the catalyst 28,30. This results in an exothermic reaction with oxygen supply in the exhaust gas that heats the catalysts 28, 30 more effectively than is possible. As a result, the graph 80 indicated by the dashed line obtained with the method according to the invention rises faster than the graph 50 obtained with the known method.

  As shown, there is a relatively large difference between the temperature graph 48 before the catalyst 28,30 and the temperature graph 50 of the central region of the catalyst 28,30 achieved using known methods. There is. As already explained, this difference, or when the temperature T of the catalysts 28, 30 and in particular the temperature at the inlet of the catalysts 28, 30 reaches a defined temperature threshold T_S, The time interval between when the temperature in the region reaches this temperature accounts for the majority of the hydrocarbon emissions released into the environment when the catalysts 28, 30 are cold. A comparison between the graph 80 shown by the dashed line obtained by the method according to the invention and the curve 48 reflecting in particular the change in the temperature T at the inlets of the catalysts 28, 30 shows that this difference is the method according to the invention. It is shown that the case is significantly smaller than the case of the known method. This directly results in a reduction in hydrocarbon emissions into the environment when the catalysts 28, 30 are still cold.

The technical field in which this invention is implemented is shown. Fig. 4 shows the time variation of the rotational speed, temperature and hydrocarbon concentration in the exhaust gas, which is performed in the known manner and in the case of the subject of the present invention. A plurality of fuel injection models are shown. 2 shows a flow chart as an example of a method according to the invention.

Claims (17)

The internal combustion engine is operated by direct fuel injection into the combustion chamber (12);
The internal combustion engine (10) is operated by suboptimal ignition angle efficiency and division of the amount of fuel injected before the start of combustion into at least two partial injections (ti_1, ti_2);
Torque loss resulting from at least one of sub-optimal ignition angle efficiency and split of injected fuel quantity is compensated by the increased charging efficiency of the combustion chamber (12),
The fuel amount and the charging efficiency are arranged in the exhaust gas region (26) of the internal combustion engine (10), which is adjusted so that the excess air lambda (L) of the combustion chamber charge is greater than 1. In the method for heating the catalyst (28, 30),
When a measure for the temperature (T) of the catalyst (28, 30) is measured and this measure for temperature (T) exceeds a predetermined temperature threshold (T_S), the amount of the exhaust gas component to be reduced is determined by the internal combustion engine. (10) being lifted by at least one intervention in the control device;
A method for heating a catalyst disposed in an exhaust gas region of an internal combustion engine.   The heating method according to claim 1, characterized in that at least one post-fuel injection (ti_3) is performed after the start of combustion in order to raise the amount of exhaust gas component to be reduced.   2. The heating method according to claim 1, wherein the ignition angle efficiency is restored to a less disadvantageous ignition angle efficiency in order to increase the amount of the exhaust gas component to be reduced.   2. A heating method according to claim 1, characterized in that the division of the fuel quantity metered in the individual fuel partial injections (t_1, t_2) is changed in order to increase the amount of exhaust gas components to be reduced. .   The heating method according to claim 1, wherein the excess air ratio lambda (L) is changed to a less lean excess air lambda (L) in order to increase the amount of exhaust gas component to be reduced.   2. A heating method according to claim 1, characterized in that a scale (T) for temperature is defined at the inlet of the catalyst (28, 30).   The heating method according to claim 6, characterized in that the exhaust gas temperature upstream of the catalyst (28, 30) is measured as a measure for the temperature (T) at the inlet of the catalyst (28, 30).   The heating method according to claim 1, characterized in that the scale for temperature (T) is determined from operating parameters of the internal combustion engine (10) using an exhaust gas temperature model.   9. A heating method according to claim 8, characterized in that a measure for the temperature (T) is determined from the signal of the temperature sensor (40) as an alternative or supplement to the measurement with the exhaust gas temperature model.   The heating method according to claim 1, characterized in that the time elapsed since the start of the internal combustion engine (10) is used as a measure for the temperature (T).   The heating method according to claim 1, characterized in that it is carried out only for a time interval of less than 30 seconds after the start of the internal combustion engine (10). The excess air lambda in the exhaust gas before the catalyst (18) is adjusted to a value greater than 1 during the heating process and the increase in the amount of exhaust gas component to be reduced The rate lambda (L) is set to be reduced from 1 to 3%,
The heating method according to claim 1.   The heating method according to claim 1, wherein the amount of the exhaust gas component to be reduced is continuously increased.   The threshold (T_S) is preset so that the catalyst (28, 30) starts to assist the catalyst in the oxidation reaction between the reducing and oxidizing exhaust gas components at this threshold temperature. The heating method according to claim 1.   15. A heating device for a catalyst arranged in an exhaust gas region of an internal combustion engine, comprising a control device (32) including means for carrying out the heating method according to claim 1. .   15. A control program for executing all the steps of the heating method according to claim 1 when executed by the control device (32).   15. A control device program product comprising a program code recorded on a machine-readable medium for implementing the heating method according to claim 1 when the program is executed on a control device (32).

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